Field of the Invention
The present invention relates to a control unit and a control method of an automatic transmission for controlling a hydraulic pressure used for a shift in the automatic transmission of an automotive vehicle, and an automotive vehicle having the control unit mounted thereon.
As this kind of control method in accordance with the prior art, for example, there is a structure described in Japanese Patent Unexamined Publication No. 9-280362. This conventional control method is structured such as to at first start an engagement of a fixed side friction device when a shift command signal is generated and next start a disengage of a disengage side friction device when recognizing a disengage timing of the disengage side friction device. Further, the disengage timing of the disengage side friction device is recognized by detecting a torque phase on the basis of a longitudinal acceleration signal of a vehicle. Here, the torque phase means a period at which a number of rotation of a turbine is not reduced and only a torque of an output shaft in the transmission is changed in the case of paying attention to a time change of the torque of the output shaft in the transmission. Further, when recognizing a disengage timing (a torque phase) of the disengage side friction device on the basis of the longitudinal acceleration signal of the vehicle, an elapsed time after the shift command signal is generated is measured, the elapsed time when the disengage timing is recognized is compared with a predetermined elapsed time and a disengage of the disengage side friction device is started for the first time when the former elapsed time is greater than the latter elapsed time, whereby an early disengage due to an erroneous recognition of the disengage timing during a rough road travelling or the like is prevented and a blowing-up of a number of rotation of the turbine is prevented.
In accordance with the control method described in Japanese Patent Unexamined Publication No. 9-280362, as mentioned above, since the disengage side friction device is disengaged for the first time when the elapsed time at which the disengage time is recognized becomes greater than the predetermined elapsed time, it is possible to prevent an early disengage due to an erroneous recognition of the disengage timing during the rough road travelling. However, in accordance with the control method described in Japanese Patent Unexamined Publication No. 9-280362, in the case that the disengage timing can not be recognized due to the rough road travelling, both of the fixed side friction device and the disengage side friction device are fixed (tied up), so that there is generated a problem that not only the shift characteristic is deteriorated but also the friction device (a clutch) is promoted to be broken.